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cpusets, hotplug, scheduler: fix scheduler domain breakage 

Commit f18f982ab ("sched: CPU hotplug events must not destroy scheduler
domains created by the cpusets") introduced a hotplug-related problem as
described below:

Upon CPU_DOWN_PREPARE,

  update_sched_domains() -> detach_destroy_domains(&cpu_online_map)

does the following:

/*
 * Force a reinitialization of the sched domains hierarchy. The domains
 * and groups cannot be updated in place without racing with the balancing
 * code, so we temporarily attach all running cpus to the NULL domain
 * which will prevent rebalancing while the sched domains are recalculated.
 */

The sched-domains should be rebuilt when a CPU_DOWN ops. has been
completed, effectively either upon CPU_DEAD{_FROZEN} (upon success) or
CPU_DOWN_FAILED{_FROZEN} (upon failure -- restore the things to their
initial state). That's what update_sched_domains() also does but only
for !CPUSETS case.

With f18f982ab, sched-domains' reinitialization is delegated to
CPUSETS code:

cpuset_handle_cpuhp() -> common_cpu_mem_hotplug_unplug() ->
rebuild_sched_domains()

Being called for CPU_UP_PREPARE and if its callback is called after
update_sched_domains()), it just negates all the work done by
update_sched_domains() -- i.e. a soon-to-be-offline cpu is included in
the sched-domains and that makes it visible for the load-balancer
while the CPU_DOWN ops. is in progress.

__migrate_live_tasks() moves the tasks off a 'dead' cpu (it's already
"offline" when this function is called).

try_to_wake_up() is called for one of these tasks from another CPU ->
the load-balancer (wake_idle()) picks up a "dead" CPU and places the
task on it. Then e.g. BUG_ON(rq->nr_running) detects this a bit later
-> oops.

Signed-off-by: Dmitry Adamushko <dmitry.adamushko@gmail.com>
Tested-by: Vegard Nossum <vegard.nossum@gmail.com>
Cc: Paul Menage <menage@google.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Paul Jackson <pj@sgi.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: miaox@cn.fujitsu.com
Cc: rostedt@goodmis.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Dmitry Adamushko 2008-07-13 02:10:29 +02:00 committed by Ingo Molnar
parent b1e387348a
commit 3e84050c81
1 changed files with 18 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
kernel/cpuset.c
View File

@ -1882,7 +1882,7 @@ static void scan_for_empty_cpusets(const struct cpuset *root)
* in order to minimize text size.
*/
static void common_cpu_mem_hotplug_unplug(void)
static void common_cpu_mem_hotplug_unplug(int rebuild_sd)
{
cgroup_lock();
@ -1894,7 +1894,8 @@ static void common_cpu_mem_hotplug_unplug(void)
* Scheduler destroys domains on hotplug events.
* Rebuild them based on the current settings.
*/
rebuild_sched_domains();
if (rebuild_sd)
rebuild_sched_domains();
cgroup_unlock();
}
@ -1912,11 +1913,22 @@ static void common_cpu_mem_hotplug_unplug(void)
static int cpuset_handle_cpuhp(struct notifier_block *unused_nb,
unsigned long phase, void *unused_cpu)
{
if (phase == CPU_DYING || phase == CPU_DYING_FROZEN)
switch (phase) {
case CPU_UP_CANCELED:
case CPU_UP_CANCELED_FROZEN:
case CPU_DOWN_FAILED:
case CPU_DOWN_FAILED_FROZEN:
case CPU_ONLINE:
case CPU_ONLINE_FROZEN:
case CPU_DEAD:
case CPU_DEAD_FROZEN:
common_cpu_mem_hotplug_unplug(1);
break;
default:
return NOTIFY_DONE;
}
common_cpu_mem_hotplug_unplug();
return 0;
return NOTIFY_OK;
}
#ifdef CONFIG_MEMORY_HOTPLUG
@ -1929,7 +1941,7 @@ static int cpuset_handle_cpuhp(struct notifier_block *unused_nb,
void cpuset_track_online_nodes(void)
{
common_cpu_mem_hotplug_unplug();
common_cpu_mem_hotplug_unplug(0);
}
#endif